The Dipstick O-Ring just needs to be changed as Rick already mentioned. Go to the parts department and ask for the O-Ring Seal for the dipstick, bring your old O-Ring with you to insure the sizes are similar.
I had the same problem with mine although mine wasn't leaking it was just pushing the dipstick up and breaking the seal.
02 C32 AMG
84 190E 2.3 5 Spd